The invention relates to a method for determining a potential of an anode and/or a potential of a cathode in a battery cell which has a negative terminal and a positive terminal.
Electrical energy can be stored by means of batteries. Batteries convert chemical reaction energy into electrical energy. In this case, a distinction is made between primary batteries and secondary batteries. Primary batteries are functional only once, whereas secondary batteries, which are also referred to as rechargeable batteries, are rechargeable. In this case, a battery comprises one or more battery cells.
So-called lithium ion battery cells, in particular, are used in a rechargeable battery. These are distinguished, inter alia, by high energy densities, thermal stability and an extremely low self-discharge. Lithium ion battery cells are used, inter alia, in motor vehicles, in particular in electric vehicles (EV), hybrid vehicles (hybrid electric vehicle, HEV) and plug-in hybrid vehicles (plug-in hybrid electric vehicle, PHEV).
Lithium ion battery cells have a positive electrode, which is also referred to as a cathode, and a negative electrode, which is also referred to as an anode. The cathode and the anode each comprise a current collector, to which an active material is applied. The active material for the cathode is a metal oxide, for example. The active material for the anode is silicon, for example. However, graphite is also widespread as an active material for anodes.
Lithium atoms are embedded in the active material of the anode. During a discharging operation of the battery cell, electrons flow in an outer circuit from the anode to the cathode. During a discharging operation, lithium ions flow from the anode to the cathode inside the battery cell. In this case, the lithium ions are reversibly transferred from the active material of the anode, which is also referred to as de-intercalation. During a charging operation of the battery cell, the lithium ions migrate from the cathode to the anode. In this case, the lithium ions are reversibly embedded in the active material of the anode again, which is also referred to as intercalation.
The electrodes of the battery cell have a film-like design and are wound, with the interposition of separator which separates the anode from the cathode, to form an electrode roll. Such an electrode roll is also referred to as a jelly roll. The electrodes can also be layered on top of one another to form an electrode stack.
The two electrodes of the electrode roll or of the electrode stack are electrically connected, by means of collectors, to poles of the battery cell which are also referred to as terminals. A battery cell generally comprises one or more electrode rolls or electrode stacks. The electrodes and the separator are penetrated by a generally liquid electrolyte. The electrolyte is conductive for the lithium ions and makes it possible to transport the lithium ions between the electrodes.
A battery cell of the generic type which comprises an anode arranged inside a housing and a cathode and two terminals is known from DE 10 2012 223 796 A1, for example.
A method for assessing a functional state of a battery cell is disclosed in DE 10 2011 117 098 A1. In this case, a cell voltage and a state of charge of the battery cell are monitored and functional state parameters of the battery cell are determined.
EP 2 762 908 A1 discloses a method for determining the power of a battery cell. In this case, the cell temperature, current and voltage, inter alia, are measured while the battery cell is being charged or discharged. An internal resistance of the battery cell is then determined from the measured data.